The main problem is this... Toyota seats don't have a single 'bracket'. There are actually two side pieces, each one of which connects between 2 bolt holes. It is the actual structure of the seat itself which connects these 2 side pieces.

Second, the irregular floor plan means that Toyota (truck) seating has to use 'tabbed' brackets (i.e., the holes are in 'tab' extensions to the main base).

If you try to transplant / adapt Toyota seats, you end up having to graft the new seats' (top portion of the...) side pieces to the bottom portion of your Taco side pieces...

The top part (connecting to the seat) is relatively simple: You could use slotted angle, Unistrut, or a drilled plate to match the required bolting scheme.

It's the bottom part (the tabbed mounting base) that's difficult.

Someone already does a good business in seat mounting - Wedge Engineering. Their brackets for a Tacoma are very well built and fit perfectly. The bad news is that they tend to cost at least $90 each....

 

I am seriously considering putting VW/Volvo/BMW seat swap on my ever growing mod list...if only money grew on trees.